Purpose :
The geometry of the iris plays an important role in the regulation of outflow of aqueous humor. The iris geometry can be described by its relative position in the anterior chamber (steepness of the iris cone: iris conicity) and its bowing (iris convexity). Scheimpflug imaging allows quantitative analysis of the anterior segment including iris conicity. We report the population-based distribution of iris conicity, investigate associated factors and test the hypothesis whether pseudophakia allows the iris to sink back.

Methods :
A population-based cross-sectional study was carried out in Germany. A comprehensive ophthalmological examination including refraction, biometry and Scheimpflug imaging was performed. Automated measurement of the iris conicity was performed. Analyses were carried out to determine independently associated systemic and ocular factors for iris conicity using a generalized estimating equation model in phakic eyes. In addition, pseudophakic and phakic eyes were compared.

Conclusions :
Associations indicate a relationship between iris conicity with lens thickness and anterior chamber depth, all risk factors known for angle closure. No association was seen with intraocular pressure indicating that the steepness of the iris does not affect regulation of the intraocular pressure in eyes without angle closure. In pseudophakic eyes, iris conicity approaches 0°, showing that cataract surgery flattens the iris position. This supports the approach of removing the lens in an eye prone to angle closure glaucoma to create a wider anterior chamber angle and to lower the risk for angle-closure.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.

Illustration of iris conicity measurement. The iris surface is approximated by a linear slope (orange line). Iris conicity is the angle alpha between this slope and the plane through the opposite anterior chamber angles (yellow line).

Illustration of iris conicity measurement. The iris surface is approximated by a linear slope (orange line). Iris conicity is the angle alpha between this slope and the plane through the opposite anterior chamber angles (yellow line).